1. Field of the Invention
The present invention relates to a method of finishing the outer surfaces of hollow aluminum shapes by barrel polishing.
2. Description of the Related Art
Hollow aluminum shapes produced by extrusion molding process etc. are usually cut diagonally, and then the outer surface is finished by surface polishing such as buffing, cutting, etc.
Also, though not for hollow aluminum shapes but for aluminum wheels, a polishing method that causes polishing medium to flow in a polishing vessel in which aluminum wheels are set, so that the aluminum wheels, while being rotated in the polishing vessel, is barrel-polished by the flow force of medium is known as disclosed in, for example, Japanese Patent No. 2740645 (Japanese Patent Application Laid-Open No. 9-234662).
However, aluminum shapes are not subjected to surface finishing by surface polishing or cutting operation due to their intricate shapes. Also, in surface finishing by buffing, it is difficult to scrape the surface of the aluminum shape uniformly; and droop would occur locally, and the scraping amount cannot be controlled quantitatively. On the other hand, in the surface finishing done by cutting operation, the range of surface finishing of the aluminum shape is restricted by the length of cutting tool, so that a defect such as weld marking is likely to occur.
Generally, hollow aluminum shapes have considerable variations in shape. Therefore, with the conventional surface finishing method, the entirety of the outer surface is not always finished uniformly.
On the other hand, it is preferable that the surface be finished with die marks thereon completely removed. Also, after the surface finishing, it is preferable that the cut surfaces of the aluminum shape do not droop, with the edge standing as it is. In the conventional surface finishing methods, the droop of the cut surfaces cannot be eliminated.
Further, though the inner surfaces of the hollow aluminum shapes do not need to be polished, it is desirable to avoid production of dents and droop on the inner surfaces. However, it is in fact impossible to avoid production of dents and droop on the inner surfaces of the aluminum shapes, and the medium used in the surface finishing sometimes remains in the hollow aluminum shapes.